EVA 4400 and mixed size Disk Group

Posted on 2009-04-21
Last Modified: 2013-11-14
We have an EVA 4400 with a single shelf containing 8 x 146gb drives.   If we add 4 x 400gb disks in the remaining bays whats the maximum capacity we can get?  Note, we require a decent level of redundancy as the EVA will we be running critical systems.

Question by:kswan_expert
    LVL 7

    Expert Comment

    if you add new HDs to your Storage, and these are of different size of previous
    (400,146) , you cannot add the 400s to any existing array. You have to build
    a new array, then split(or take whole) this in LV(s), then LUN(s).
    You can build a RAID5 having 400x3GB resultant, or RAID10 (=400x2), or
    2 RAID1 (2 x 400).

    Does just one server access the storage ?

    If you build another Array->Lun, you'll see this as a new disk in server
    (which OS ?), partition it(Unix or Win), Format(U/W with diff commands) and
    create a new volume (Letter in Win F:) or mount this partition under an existing
    directory (in Unix this is the sole possible method) but you can also do this in Win
    OS. If you need space on your C: or E: disk, and you know all growing space will
    concentrate in a dir, you can move these in anothe location, mount new partition under this dir, re-copy moved files in that dir. Physically the files will go in the new 4x400GBHDs, even OS continues to write undes C:\MyApplication.

    LVL 55

    Expert Comment

    You can have mixed drive sizes in an EVA disk group but it's not a good idea since they will have many more disks accesses than the current disks and will therefore becone "hot" disks. re-levelling based on I/O will be competing with re-levelling based on capacity usage. Sparing as well as parity will also eat up the size of the largest disk in the group.

    So assuming vRAID5 with a sparing level of one, 146*8 + 400*4 - 400(parity) -400 (spare) = 1968GB (of course occupancy alarm will be going potty by that time as it goes off when there is 15% space left)

    Assuming vRAID5 with sparing of two, 146*8 + 400*4 -400(parity) -2*400(spare) = 1568GB.

    I'm afraid that what dolomiti says doesn't work since you cannot make a disk group with less than 8 disks on an EVA.

    See also this thread,

    LVL 55

    Accepted Solution

    Oops, knock 400GB off the above calcs, vRAID 5 uses 1 parity for every 8 disks in the disk group so parity will take up 800GB in each case, not 400GB.

    Author Comment

    Cheers Andy.  

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